1. Technical Field
This invention relates generally to wet shaving apparatus, and more specifically to razor cartridges having an improved skin engaging device. The present invention resides broadly in providing skin engaging cap and/or guard surfaces with configurations which deliver a shaving aid as the razor is moved across the skin.
2. Background Information
In shaving systems of the wet shave type, factors that include but are not limited to the frictional drag of the razor across the skin, the force needed to sever hairs, and irritation of pre-existing skin damage can create a degree of shaving discomfort. Discomfort, and other problems accompanying wet shaving systems, can be alleviated by the application of shaving aids to the skin. Shaving aids can be applied prior to, during, or after shaving. A number of problems accompany the use of pre- and post-applied shaving aids. Pre-applied shaving aids can evaporate, can be carried away from the application site by repeated strokes of the razor or can be washed away from the application site by the application of water. Post-applied shaving aids are not present on the skin during shaving and thus their application can be too late to prevent an unwanted affect. Both pre-applied and post-applied shaving aids add additional steps to the shaving process.
Many previous proposals have been made to incorporate a shaving aid, for example a lubricant, whisker softener, razor cleanser, medicinal agent, cosmetic agent or combination thereof, into a razor for example by depositing a shaving aid in a recess on the razor, by incorporating a shaving aid directly into one or more molded polymeric components of the razor, by adhesively securing a shaving aid composite to the razor, and by use of a mechanical connection between a shaving aid composite and the razor. A water-soluble shaving aid, e.g. polyethylene oxide, has been mixed with water insoluble matrix material, for example a polystyrene polymer, to form an insoluble polymer/soluble shaving aid composite as disclosed in U.S. Pat. No. 4,170,821 to Booth and U.S. Pat. No. 5,113,585 to Rogers. The composite has been mounted on razor and shaving cartridge structures, adjacent the shaving edge or edges, of single or multiple blade shaving systems. Upon exposure to water, the water-soluble shaving aid leaches from the composite onto the skin. These composites tend to release large amounts of shaving aid in the first few shaves and dramatically less shaving aid in subsequent shaves. Furthermore, extruded composites with relatively large amounts of shaving aid (up to 80% by weight) and relatively low amounts of water insoluble matrix material (as little as 20% by weight) are relatively weak and have a tendency towards mechanical failure, both in manufacture and assembly and in use. Increased mechanical strength can be obtained with increased amounts of the insoluble matrix material. However, such increase reduces the proportion of shaving aid material in the composite and the releasability of the shaving aid material.
Commercial lubricating strips, especially those with high levels of polyethylene oxide lubricant like those described in the aforementioned Patents tend to deteriorate after use. Leach rate varies during the course of shaving and typically about 50% of the polyethylene oxide can be trapped in the strip. The selection of the polyethylene oxide carrier (i.e., the non-water soluble matrix material) is limited to a carrier that has a low melting or softening temperature and is at least partially miscible with polyethylene oxide. In addition, because the strip is made at a high temperature of approximately 180° C., additives such as fragrances and plasticizers are difficult to incorporate in the strips.
U.S. Pat. No. 6,298,558 to Tseng et al, the subject matter of which is incorporated for reference herein in its entirety, discloses an improved device for use in razor cartridge assemblies and shaving systems of the wet shave type. In one embodiment, there is provided a two-component, control-release shaving device consisting of a sheath layer made from thermoplastic resins with openings therein and a core region containing internal shaving aids. Potentially, the device can maintain surface appearance, control-release the shaving aids, minimize the degradation of the shaving aids, minimize the shaving aids trapped in a strip and provide a device which is easy to manufacture and/or which is easily integrated with a razor cartridge system. The '558 Patent discloses a manufacturing method whereby the device is produced by providing a two-component extrusion, or coextrusion, that is cut to length suitable for implant into or onto the body of a razor blade cartridge. Cutting-to-length exposes the core portion at both ends of the device. Upon contact with water in use, the device can undergo accelerated leaching of the shaving aid from the exposed ends of the core and leaching in a direction where the shaving aid is not deposited on the skin and is thus wasted. As many shaving aids tend to swell upon contact with water, the exposed ends of the device can expand uncontrollably which can lead to premature failure of the entire device.
Based on the foregoing, it is desirous to provide a coextruded device for the delivery of shaving aid material(s) for a razor cartridge or shaving system having a sheath of a water insoluble polymer and a core including a water soluble shaving aid. The device is cut to length and the end portions are closed to inhibit the ingress of water in use and inhibit premature leaching of the shaving aid or premature failure of the device.